Double-suction centrifugal fan

Abstract

A double-suction centrifugal fan includes: a first impeller coupled to a shaft; a second impeller provided with a second inlet port opened opposite to an electric motor and coupled to the shaft at a position farther from the electric motor than the first impeller; a first bell mouth connected to a first inlet port of the first impeller, and a second bell mouth connected to the second inlet port of the second impeller. An axial length L2 of the second bell mouth is greater than an axial length L1 of the first bell mouth.

The invention claimed is: 
     
       1. A double-suction centrifugal fan, comprising:
 an electric motor having a shaft; 
 a first impeller provided with a first inlet port opened toward the electric motor, and coupled to the shaft; 
 a second impeller provided with a second inlet port opened opposite to the electric motor, and coupled to the shaft at a position farther from the electric motor than the first impeller; 
 a first bell mouth provided at the first inlet port of the first impeller; and 
 a second bell mouth provided at the second inlet port of the second impeller, wherein 
 the first impeller includes a first shroud having the first inlet port formed therein and a portion that overlaps the first bell mouth over an entire periphery, 
 the first shroud has an inner diameter decreasing toward a side of the first inlet port, 
 the second impeller includes a second shroud having the second inlet port formed therein and a portion that overlaps the second bell mouth over an entire periphery, 
 the second shroud has an inner diameter decreasing toward a side of the second inlet port, and 
 an axial length L 2  of the second bell mouth is greater than an axial length L 1  of the first bell mouth. 
 
     
     
       2. The double-suction centrifugal fan of  claim 1 , wherein
 each of the first bell mouth and the second bell mouth has a tubular straight portion extending along an axis thereof, and 
 a length Ls 2  of the straight portion of the second bell mouth is greater than a length Ls 1  of the straight portion of the first bell mouth. 
 
     
     
       3. The double-suction centrifugal fan of  claim 1 , wherein
 an inner diameter d 2  of an air inflow port of the second bell mouth is greater than an inner diameter d 1  of an air inflow port of the first bell mouth. 
 
     
     
       4. The double-suction centrifugal fan of  claim 2 , wherein
 an inner diameter d 2  of an air inflow port of the second bell mouth is greater than an inner diameter d 1  of an air inflow port of the first bell mouth.